This invention relates to a novel bitumen mixture and a high performance prefabricated waterproofing membrane useful for roofing which is obtained by impregnating different layers of reinforcing material with the bitumen mixture. More particularly, the invention relates to a novel bitumen mixture and a waterproofing membrane comprising a series of reinforcing layers including a polyester mat, a mat of fiberglass and a fiberglass net. Each reinforcing layer is impregnated with bitumen mixed with a thermoplastic polymer wherein the polymer is selected from the group consisting of an amorphous copolymer of ethylene/propylene, atactic polypropylene, polyisobutylene and styrene-butadiene-styrene block copolymer. The mixture has a minimum ring and ball softening point of about 105.degree. C. and preferably 155.degree. C. Preferably the bitumen contains amorphous ethylene/propylene copolymer, a mixture of atactic polypropylene polymer and ethylene propylene copolymer containing mineral acid and isotactic polypropylene.
For almost a century bituminous roofing membranes have been used in the United States to protect buildings, their contents and the occupants from the weather. The most common type of bituminous roofing membranes consist of two to five layers of felt or fabric which during application to the roof are made to adhere together with bituminous material, such as tar, pitch or asphalt. The fabrics or felts may contain organic material, asbestos or glass. In general, these types of roofing membrane have been the source of problems for manufacturers of the membrane, roof designers, appliers and users. The incidence of failures in flat roof waterproofing membranes has increased in the order of 30 percent in that time period. The problems have been attributed in part to poor design, inadequate materials and improper workmanship, but many believe that the problem is more fundamental.
Conventional roofing membranes were originally developed in order to cover concrete and wood roofs which formed a relatively stable rigid base for the roofing membrane. Today roofs are being made of more flexible lightweight material and are often formed from prefabricated sheets or panels many of which have highly efficient thermal insulation. These changes in the thermal properties of the building materials have completely altered the temperature environment of the roofing membrane. This thermal change coupled with resulting movement in the joints of the roof and the insulation, places substantial local stress on conventional roofing membranes which were originally designed with relatively low tensile strength and elasticity.
An additional problem associated with traditional roofing material is that it requires about 12 lbs/m.sup.2 of bitumen or other petroleum based products. Due to the high cost of petroleum and the efforts to conserve petroleum, it is also desirable to decrease the amount of petroleum based products used in roofing membranes.
Some attempts by others in the roofing field to produce an improved roofing material are described in U.S. Pat. Nos. 3,741,856; 3,753,938 and 3,937,640. U.S. Pat. No. 3,741,856 to Hurst issued Jan. 26, 1973, describes a bitumen waterproofing sheet which has a polyethylene support layer and a pressure sensitive adhesive backing. The Montague patent, U.S. Pat. No. 3,753,938, issued Aug. 21, 1973, describes a special roofing material which contains a mixture of bitumen, a synthetic elastomeric material which is predominantly chlorosulphonated polyethylene and fibrous material such as filaments of fiberglass or other synthetic bituminous roofing membrane comprising a base sheet of a synthetic polymer and one or more layers of bitumen. In addition, another roofing membrane has been developed in Europe in an attempt to meet the new requirements of modern roof construction and is the subject of patents in Luxembourg (No. 69480), France (No. 7505703) and Italy (20554A/75). (See also Impermeabilizzazione Delle Construzioni, Romolo Gorgati, 1974 pp. 63-64). The prefabricated roofing membrane developed in Europe contains a polyester mat and a fiberglass mat both impregnated with polymer modified bitumen. Although this roofing material has performed satisfactorily in some applications, it does not have the necessary tensile strength, dimensional stability, resistance to puncture, oxidation and aging needed for demanding modern roofing applications.
It is the object of this invention to provide a novel bitumen mixture and a novel waterproofing membrane using that bitumen mixture which has superior mechanical and physical-chemical characteristics which meet the preliminary performance criteria for bituminous membrane roofing published by the U.S. Department of Commerce/National Bureau of Standards and to achieve these superior characteristics without substantially increasing the total weight, cost of the roofing membrane or the amount of petroleum based product used.